This invention relates to a manually powered vehicle and more particularly to a manually powered vehicle such as a bicycle with an assist engine for assisting in the operation of the vehicle.
A wide variety of vehicles have been proposed which are designed to be primarily powered by manual power input of the rider. In order to expand the use of these types of vehicles, it has also been proposed to provide various forms of power assist. These power-assist devices incorporate a prime mover, such as an electric motor or an internal combustion engine, which can be operated so as to assist in the manual propulsion of the vehicle. One very successful power-assisted vehicle of this type employs a sensor that senses the actual manual force input by the operator, and then operates the prime mover so as to provide an assist force that is proportional to the manual force.
The advantage of this type of system is that the rider still maintains a "feel" in operating the vehicle. That is, the operator's manual input of force is necessary in order to have the vehicle propelled, and thus the exercise value of the manual propulsion system is maintained. By utilizing the power assist, this type of vehicle can be utilized by persons of varying physical capabilities. Also there is less need to govern the speed of the vehicle since the operator must always input a force to have any power assist.
With these types of power-assist mechanisms, the device generally utilizes a form of force sensor which senses the actual manual force input by the operator. This manual input force is then utilized to provide a control signal for controlling the appropriate amount of assist by the prime mover.
However, many of these types of vehicles are operated by mechanisms wherein the operator input is not constant. For example, many vehicles of this type utilize a pedal-operated crank mechanism for their manual input. Because of the angular relationship of the crank mechanism, the actual force varies cyclically during a single revolution. Thus, the power assist will also vary cyclically in the same manner.
This presents a particular problem when the prime mover is an internal combustion engine. If the engine output is varied cyclically along with the manual force, then because of the inherent uneven characteristics and quick response of internal combustion engines, a jerky operation will result.
It is, therefore, a principal object of this invention to provide an improved power-assisted vehicle that employs a powering internal combustion engine.
It is a further object of this invention to provide an improved internal combustion engine power-assisted vehicle wherein the power assist is proportional to the manual force input, but a smoothing of the applied power assist is accomplished to avoid jerky operation.
In addition to the problem of the cyclically varying manual input, these types of vehicles also employ brake systems for retarding the forward motion of the vehicle. There may be times when the brake is applied, and also some force may nevertheless be applied to the pedals. For example, the operator may be holding the vehicle stationary, but nevertheless may apply some force to the pedals. Since the force-sensing mechanism will sense an output, then the power assist may energize the engine and undesirable results may occur.
It is, therefore, a still further object of this invention to provide a power-assisted vehicle wherein the application of power assist can be totally disabled when the brake is applied.
It is a further object of this invention to provide an internal combustion engine-assisted manually operated vehicle wherein the relationship between the power assist and the operator force can be altered to suit certain conditions.